“If you live together with someone for ten years in a committed way, or you’ve been married to someone for ten years in a committed way, you’re probably dealing with the same kinds of dynamics and the same kinds of issues,” he notes, “and you need the same kinds of skills to make it work.”

And Williams, the Drexel professor, thinks unmarried, committed parenting is not necessarily a bad scenario.

“If I think about my training in psychotherapy, there are many people who get married who shouldn’t get married,” he says. “There are many people who feel pressured to get married. And the impact on the child can be significant.”